The present invention relates to a method and apparatus for assembling universal joints.
Universal joints and method for assembling them are not new per se. For example, in West German Offenlegunsschrift No. 1,527,557, the bearings are pressed into the bearing bores of the fork of a joint fork by means of floating pressure units without any reactive force and fixed in place axially, for example, by peening. The joint cross in these assemblies is positioned so that after the pressing and peening operation a finished mounting results. It is desirable in these assemblies that the joint cross not have any axial play and should have a braking moment in the pivoting direction, which moment is often called the bending moment. The bending moment is obtained by reason of the fact that the bearings are fixed in place while the pretensioned forks are spread apart and the bottoms of the cups of these bearings are in contact with the universal joint pins. In presently known assemblies, the bearings are first pressed simultaneously into the bearing bores and during this process, the forks are supported from behind in each instance by a hook-like support element attached to the pressure unit so that the pressure can thus act on the bearings without any reaction from the pressing tool. Thus, when the bearings in these known assemblies are in contact with the pins of the joint cross, a further application of pressure causes the forks to spread whereby the floating pressure units are activated outwardly. The displacement distance is limited by adjustable stops wherein the pretension obtained by means of the spreading distance of the fork arms can be determined in advance.
A particular disadvantage of the above described prior known universal joint assemblies and the method for assembling them is that since manufacturing tolerances result in cross sectional and/or structural differences between the two fork arms (the joint fork in cross section is an unworked casting), these differences result in different restorative forces or pretensions in the fork arms even if the arms are spread by the same amount. The difference between the restorative forces acts by way of the bearings directly on the joint cross and shifts the joint cross out of its precentered position. This results in an impermissible misalignment of the centers of the two joint parts with respect to each other which can no longer be optimally compensated even by balancing these parts individually since the joint parts must be bent toward each other in order to function properly.
The differences between restorative forces also produces large differences in the bending moment from one joint to the next. This defect is aggravated even more by the unavoidable manufacturing tolerances of the joint forks amongst themselves and not merely between the fork arms of a single joint fork.
Further disadvantages of the prior known designs are evident when differences occur in the tolerances of the fit between the bearing and bearing bore in the two fork arms. In this instance, there are differences in the pressing forces which as a result of the internal stress in the fork arms results in pretension particularly during the spreading phase which differs sharply from the adjusted spreading distance. This means that the center misalignment of the joint parts can become even greater. The same defect occurs in the case of differences in the peening forces. Without precise pairing of the two parts, which must be done individually for each fork arm before each assembly, these errors are virtually impossible to avoid. Accordingly, good assembly results can be achieved with the prior known methods only under ideal conditions, i.e. when the fork arms are completely free of tolerances between themselves and from fork to fork and when correspondingly tolerance-free bearings are also available. As a practical matter, these conditions are virtually impossible in actual mass production environments.
In accordance with another prior known assembly of the type shown in West German Registered Design No. 1,965,040, the fork arms are spread with the requisite pretensioning force before the bearings are pressed in place and the forks are fixed in this position by means of mechanical elements. This method, therefore, prevents occurrence of differences in the restorative forces in the fork arms resulting from cross sectional and material variations. However, when different pressing or peening forces are required for the bearing, even this prior device has an appreciable reverse effect on the adjusted spread of the fork arms. Consequently, even though better results are obtained with this known device, an intolerable misalignment of the centers can also be anticipated.